Semiautomatic telephone switching system arranged for selective alternating current or direct current key pulsing



V. E 3 M N 8 1 l R 2 t DQ K 0 7 C, H 8 h 2 q M A 6, s 2m u k B. m m P f A S H Dn 4 h. h Mm .|F Law.. W M mm u QQ Smm YR t S w m .\HU m u (www Imm.. H Mwnm IMK w CSRT Mwm .Num Bm u PEC ENT um L Emu TER m. @t N um CLT. IED ms mt mm MF mfw A m 9 p mw 1. .i w1 i 6 w w l. nw m. www e QRMQ 1.. s m. o d .w m F F Feb. 10, 1953 B MoK|M Y 2,628,283

SEMIAUTOMATIC TELEPHONE SWITCI-IING SYSTEM ARRANGED -FOR SELECTIVE ALTERNATING CURRENT OR DIRECT CURRENT KEY PULSING Filed Sept. 16, 1948 4 Sheets-Sheet 2 /NVENTOR B. Mc KIM ATTORNEY Feb. 10, 1953 B McKlM 2,628,283

SEMIAUTOMATIC TELEPHONE SWITCHING SYSTEM ARRANGED FOR SELECTIVE ALTERNATING CURRENTOR DIRECT CURRENT KEY PULSING Filed Sept. 16, 1948 n 4 Sheets-Sheet 5 @QCM ATTORNEK Feb. 10, 1953 B. McKlM SEMIAUTOMATIC TELEPHONE SWITCHING SYSTEM ARRANGED FOR SELECTIVE ALTERNATING CURRENT OR DIRECT CURRENT KEY PULSING Filed sept.` 1e, 194e 4 Sheets-Sheet 4 /NVENTOR 8. Mc K/M ATTORNEY Patented Feb. 10, 1953 UNITED STATES PATENT orties RENT KEY PUIgsING 4 B'uito'n. .-McKiim. East Orange,` fN. J.; assigner .to liilelephone Laboratories; Incorporated, New York, N. Y., a corporation of New York d Application September 16, 1948, Serial o. 19,2588- 7 claims. (C1. iislaz') This invention relates to telepl'io'ne systems and more particularly to toll switching systems.

One of the primary objectsY of theinvention is to improveV the circuit arrangement for toll switchboards whereby operation of said toll switchboard is made more fiexible'.

A further object of -the invention is to'- simplify toll switchboard systems inl which bothfdir'ect current and multifrequency key pulsing are einployed. d

There is in the prior art one or more circuit arrangements whereby direct current keyfpuls ing is attained. Byway of example, United States Patent No. 1,780,906, grantedv to,` W.-W. Carpenter and R. E. Hersey NoV'mberLILllQSU, is referred to. In that iiaatent'` the operators key-set transmits marginal and IV.reverse direct current impulses over the' talking conductors of the cord circuit and the trunk, then through the link circuit to the responsive quipmentji'n the sender. There is also disclosed 4in the .prior art a circuit designed to transmit multifrequency. key pulses over the talking: cord circuits and. trunks to the sender. For aidetail'eddescription of the circuit'and operationthereot the reader is referred to United States Patent No'..2,288,25"1, granted to' Paul B. Murphy June"`30f, 1942'. l

Prior to applicants' invention a'AVV toll. switch` board was designed to use either direct current key pulsing or multifrequency key. pulsing;`` but not both. For reasons disclosed in Patenti No. 2,288,251, it has" been foundthat for certain purposes multifrequency key pulsingsuperior to direct current key pulsing.l .This isi-largely due to the factv thattherear certain losses incident to the transmission of direct' current' impulses over longcablev paths. and tothe` fact that certain digit codes involvetheh transmission of impulses of differentv voltages requiringl response of sensitive and marginal responsive rei lays in the sender.

Conversely there' are" very good reasonsrwhy direct current key pulsing isi-.superior to .multifrequency key pulsing: und'erdilerent circumstances. There are in commercialuse'several' thousands of toll switchlltjia'rds'"which'v are designed to handle direct current key' pulsing, but many of these tollv switchboard's'" arer becoming' overburdened by heavier telephonef` toll traiiic. It is believed that therefw'llbe the'A future agreat deal of decenti"aliaatiiniF of* toll(opfera`-r tion which will make it desirable to'utilia'e these direct current tqu wineplacards'I :of muiufre= quency keyy pulsing withmas'i little kclia'ngev 1n said SYSTEM ARRANGED FOR -1 sjELEC'rIvE ALTERN `TING CURRENT 0R DIRECT CUR- maintain vequipment for the exclusive` use of. multifrequency key pulsing would be both very eiipnsive and time consumingf y This invention embodiesa'n operators key-set circuit-thatican send either. direct currentor multi'frequency' key pulses, multifrequency key pulses being transmitted only in case the trunk circuit over which it is desired to send avsignal and to which one of the cordsvat the position circuit is connected, is arranged to indicate to the position circuit that vthe said trunk terminates in anoilice arranged.ormultifrequency signaling. Similarly, directv currentkey impulses are transmitted to a trunk circuitonly when that trunkcircuity and the terminating otiice are' adapted to receive direct current key pulses. Consequently this invention will automatically. enable transmission of either multifrequency or direct current key pulsing signals from one keyset with very little change in existing circuits, Whereas the prior art required tWo circuits With additional appartaus. .f l IA* clearV and complete understanding .of the invention will b'e` facilitated `by. considering a telephonel system in whichmthe invention and its features' ar eembodied, one. suchzsystem beingv shown in the drawings which constitute a part of'tnis specification.

Referring to the-drawings;A l Figs l andlA represent schematicallyartelephoneVY system comprising a manual switchboard includingk operators cord,` position and telephone circuits, oi'itgoingl truck circuits, and automatic switching-equipment inanother oice for lcompleting desired Vtalking conversations between calling and called subscriber stations;y Fig. 1

further shows,v in diagrammatic form, key pulse,

ing register, sender and linkvcircuits associated witli outgoing trunk circuitsv arranged for al-4 ternating current key pulsing; andvFig. 1A,- fur. ther' shows trunk,link and Lkey pulsing sender circuits arranged for direct current key pulsing;' Y

Figs'. 2, 3 ande lshow a'. key setY circuit for use by an operator in extendingY connections to" subscribers in theautomatic cnice; and...

Fig.l 5 shows thek relative position in which the drawings are to be placedY to form an operative arrangement. f

In Fig; 1 a calling subscribers station is shown c'onnected't'ol a trunk circuit 3' terminating in a jackv at anoperatorposition, one. endo'f v a cord 2 being inserted in the jack to answer the call.v4 y v E A NOnly as muchoi Vthe cord, positiongand trunk To'construct'and's" circuits` are shown" as'are required for a complete description of the invention. Trunk circuit 4, in Fig. 1, is arranged to transmit multifrequency key pulses to a sender. Since this type circuit is well known in the prior art a complete drawing or description thereof is not deemed necessary. Reference is made to the Murphy patent cited hereinbefore. Ground is connected to the ring lead of the front plug at the time it is connected to trunk 4. As will be explained later this ground completes the circuit for the winding of test relay D to operate relay D and prepare the key-set circuit for transmission of multifrequency key pulses. Trunk circuit 6, in Fig. 1A, is adapted to transmit direct current key pulses to a sender. This type circuit is also well known in the prior art and the drawing and description thereof are not detailed. The key pulse sender 'I is also designed to receive direct current key pulses. Shown in key pulse sender I are relays KC, TM, TP, TS, RM, RP, RS, and ON, and 24-volt batteries 324 and 325. The relays KC, TM, TP, TS, RM, RP, and RS are individually and independently operated by various combinations of battery, resistance battery, ground, and resistance ground impulses from the key-set shown in Fig, 3. Fig. 1 also shows a block diagram 326 representing position and telephone circuits. Position and telephone circuits such as used here are also well known in the prior art and therefore detailed drawings or description are not considered necessary. Reference is made to United States Patent 2,276,515, issued March 17, 1942, to T. D. Robb for a full description of such circuits.

Referring to Fig. 2, relay F and relay R are respectively associated with the front cord circuit and the rear cord circuit. Relay F and relay R are utilized in both direct current and multifrequency key pulsing. If the key pulsing is to be done over the rear cord, relay Ris operated and relay F is not operated. If the key is pulsing is to be done over the front cord then relay F is operated and relay R remains unoperated. It will be assumed that relay F is operated for purposes of this disclosure. The purpose of relay F is to connect the key-set to the trunk circuit and Vprepare said key-setfor determination of the type key pulsing to be transmitted to said trunk. This operation will be`described in detail later. Relay MF is utilized when the trunk circuit 4 is arranged for receiving multifrequency key pulses. Operation of relay MF acting in cooperation with other relays KP, KPI .and SAI, prepares the key-set for the transmission of multifrequency key pulses. The front and rear cord key pulsing keys KPF and KPR are operated manually by the operator. Their function is to operate relay F or relay R. respectively, and also relay KP. Relay KP performs no useful function on a call requiring a direct' current key pulse but on calls requiring multifrequency key pulsing the KP relay is utilized to transmit a signal to the sender to notify the'sender that multifrequency key pulsing is about to begin. The KST key is oper- 6 ated manually bythe operator on direct currentkey pulsing after the numerical keys shown in Fig. 3 have been'operated. This will cause relay ST to operate and connect ground to `the.

tip conductor andresistance battery to the ring conductor to indicate to the sender that no more digits'will be keyed. Similarly, in the case of multifrequencykey pulsing operation of manual key KST operates relay ST in Fig. 3 to transmit a signal which indicates tothe sender that:

no more digits will be keyed. In Fig. 3 relays MFI and MP2 in operating transfer the leads of the numerical keys from the battery and ground patentials used for direct current pulsing to the alternating-current sources required for multifrequency pulsing.l Relay MP2 also completes the circuit for operating relay SAI shown in Fig. 4. The Various alternating-current sources a, b, c, d, e, f, used in multifrequency pulsing are also shown in Fig. 3. Numerical keys 83 through 92 are operated by the operator to -transmit either direct current or multifrequency pulsing to the trunk circuit being used. Sender lamp S is operatedvupon operation of relay SAI of Fig. 4 and indicates to the operator that the sender is ready to receive key pulses from the key-set. y

In Fig. 4 relays D and DI are associated both with direct current and multifrequency key pulsing. DI is a slow-to-release relay which will not release when direct current key pulsing is required by the trunk circuit. Relay D is operated when its winding circuit is completed by ground being applied to the ring lead in the trunk circuit. In the case of a trunk circuit requiring direct current pulsing the said ground is removed and relay D becomes deenergized before relay DI has time to release. Thus relay MF will not operate. In the case where the trunk circuit requires multifrequency key pulsing the Aground applied to the winding of relay D to complete the circuit of said winding is not removed from said winding and relay DI has suiiicient .time to release, thus causing operation of relay MF.

In direct current key pulsing, relay SAI is operated by relay SA which is operated when the direct current sender is attached to the trunk circuit. Operation of yrelay SAI prepares the key-set circuit -for transmission of impulses and noties the key monitoring circuit (not shown) that the sender .is ready to receive registrations from the key-set. Detailsof this operation will be described in detailclater. .For both direct current and multifrequency key pulsing operation of relay SAI prepares for the later operation of relay P. Relay 5P is a polarized relay with three windings. Its functionis to return the entire key-set circuit to` normal condition after registration vhas beenY completed; Relay KD is operated by relay P to act. in cooperation with relay P in returning the key-set circuit to normal condition.V

The operation of the circuit will now be described in greater detail. It will be assumed that the trunk circuit involved in this call requires a direct current key pulse registration. When the front cord is plugged into an outgoing trunk circuit the said trunk circuit starts a two-way link circuit hunting for the trunk and'for an idle sender. Ground is connectedv to:1ead1DFI by means well known in thetelephone art. Operation ofthe cord talking` key (not shown) causes relays in the position circuit to function to loop leads DFI andsDF together and to connect ground to lead DH. The'operation of the talking key and position circuitY is well known in the prior art and the detailed operation of them Will not be discussed here. Ground on lead DH causes relay DI to operate by establishing a circuit through lead 8, through armature of relay D, through lead 9, through the winding of relay DI, to negative battery. It is to be noted here that the coreV of relay DI must become saturated.befcrirelarloigerates so that relay;

DI will not be released by relay D while said relay D is, testing for ground on the ring'- conductor Operation of the front key pulsing key KPF connects ground on the DFA lead to the winding of relay KP through leads Il and I6 and to the winding of relay F through lead I2. Relay F operates by reason of accmplete'd crcuitthrough negative battery I3, lead I4, lead I5, Winding oi relay F, through lead I2 to ground on lead DF. A locking circuit for relay F 'is then established from the same negative` battery, through leads It and I5, through the Winding` of relay F; and then through contact I6 to ground on lead DF. The Winding of relay KP is energized through` a circuit extending from negative lbattery,r Winding of relay KP, lead IIl, lead II, through contacts of' front key pulsing key KPF to ground on lead DF. Operation of said relay KP establishes a locking circuit for said relay KP from battery, through contact or relay KR lead 32,9, lead 328, contact 21 of relay KPI, to ground on lead 2l. The ground on lead 2I is causedby. the operation of relay F which closes contact vI9 and extends ground potential through leads i9 and 20 to lead 2 i.

When relay F operates, it actuates contacts which, (l) light the KF lamp through contact 23 to indicate that the key-set is associated with the front cord; (2) open the operating, circuit for relay R; (3) supply ground to the key-set circuit through lead 26 andy for locking up relays SAl, KP and KD. The locking circuit for relay SAI will be described later. The locking circuit i'or relay KP has been` heretofore described. For relay KD the locking circuit extends from neg ative battery Sii, through Winding of relay KD, lead 3l, lead 38, leadY 39, contacta() of relay SAL lead 4I, lead 42, and contacty 43' (when closed) to ground. Operation of relay-Falso provides 69-ohm resistance battery to the winding of relay SA from ground, through contact lili (when closed), resistance 45, lead t, Contact 41, battery 4S, to ground. In addition, relay F performs the following functions when itV operates, (4) connects ground tothey DH lead through Contact t9 so as to hold the keypulsing circuit locked to the cord circuit even though the talking key (not shown) should be restored to its normal position; (5) disconnects the tip and ring leads of the cord circuit from the position circuit and connects them to the key pulsingvcircuit. The lead FT now extends from the tip lead` in the cord circuit through contact 22 of relay F, to leadSI. The lead FR now extends from the ring lead in the cord circuit through contact 5I) to lead 52. Continuing, the operation of relay F connects biasing battery 53 through resistance X to winding IIQ of relay P through conductor 54, and also establishes a circuit from negative 24-volt battery through contact 41, conductor 55, Winding of relay D, contact 55 oferelay SAI, conductor 51, contact 53 of relay MF, conductor 52, contact 50 of relay F, conductor FR, to the ring conductor of the front cord.

As soon as the link circuit in Fig, lA has found an idle circuit and has connected the direct current key pulsing sender 1 tothe trunk circuit 6, battery :t8 through relay D is connected over the ring conductor through the link in the path just described and then through the winding of relay KC, the contact of relay ON, which is closed at this time by means well known in the telephone art, and then to ground. RelayD operates and opens theopcrating.circuiti@ relay` Dl. Since relay Dl has a slovJ-to-reiease characteristic,. it does not release immedi/otely. Be fore suici'ent time has elapsed to effect a release of relay DI, however, relay KC in the. sender operates to open contact. 59 'and close contact Si, thus removing ground 4from the Winding of relay D 'and replacing.said ground with a 2st-volt negative battery Which is equal to and opposed in polarity to Zbl-volt battery 48", causing d'eenergization of relay D. Relay DI, therefore, remains` energized. Inv operating, relay KC disconnects itself from the ringconductor by openi ing contac, and relay KC-l theeaftel energizedv by battery 82". Battery 326` isconnected to the tip conductor when contact 69 closes Ato operate relay SA .by a circuit extending from ground, through the Winding of" relay SA, conductor 6I, 'contact`, 'o`frelay MF, conductor 5l, contact 22 of relay Fyconductci FT.; the tip conductor of 'trunk circuit 6, through contact 6c, and the windings of relays TM, TP, TS, to negative battery.` Relay SA,` in operating, locks under control of relayl F by virtue of contact 'c1 of relay F. Operation of said relay SA causes relay SAi to operate by establishing a vcircuit from negative battery, through the winding' of relay SAI, conductor '28, contact 29 of relay'SA, conductor 36, contact |10 of relay KD, to ground on lead 33. A locking' circuit for relay SAI is new established from negative battery 3*, throughA the winding, ci' "relay SAI conductor 28, contactr 29' of relay SA', conductorsv 39 and 3i, contact 34 of relay SAI, toV ground onKA lead' 32. Relay SAI, in operating 'disconnectsrelay'D from the ring conductor" FR' by openingv contactv 56; connects the tip6I and ring 51 conductors ofthe cord circuit to' the key-set keys; connects-Sevolt battery 333 through ballastl lamp J 'Ito the" keyset keys in'placeof' the lgroundl through resistance C. This circuit can` be' ltraced from-` negative battery 333, through ballast lamp J, conductor 62, contact 63 ofrelay SAI, conductor-64, conductors 65 and 66, contacts61, 68 and 69 of relays MFI and MP2, conductorsv 19, 'II and 12, and thence to the keys of the key-set. Operation of relay ,SAI also opens the circuit from thejkey'- set keys to relay KD by `virtue of contact 13 being opened, closes contacts 14, 15, and' 16 for* the later operationofrelay/P, and lights the-sender lamp S by a circuit extending from negative battery 11, through resistance 18, through sender lamp S, conductor 19, contact 80, to ground.

The lighting f of the sender lamp indicates' to the key-set operatorthat the' sender is ready to receive registrations from the key-set. The voperator depresses the numerical keys shown vin Fig. 3 in the order corresponding `to the code and number to be registered. Variouscombinations of light and heavy'battery and ground pulses are transmitted over the tip and ring conductors to the sender register relays. These combinations are such-that relayfPwill `not'b'eoperated at this time. For an example, vlet it` befassu'med that key 65 is operated. Contact ismade between conductors 91 and 96 and betweenconductors III and IDG. Conductor l91 'can'V be traced frornflvolt battery333, through lamp J, conductor 62, contact- 63 of relay-SAI. conductor 64; resistance |01, conductor G6, contactl, conductor'l', to conductor 91. Thus negative signaling battery through resistance |61' is impressed on lconductor 96 which can be traced'to the/tip conductor through conductor 95,'1a back contact' of`relay MFI, conductor 94, conductor 93', `contact .|63 'o'f relay SA`I'conductr.61|;,back cn'taotof relay.

MF, conductor 5I, contact 22 of relay F, conductor FT, to the tip conductor of the cord and jack, back contact of relay 3|6 of trunk circuit 6, contact of relay K5, and windings of relays TM, TP, and TS to battery 324. Conductor |06 is at ground potential by virtue of a circuit extending froni ground, through contact I9 of relay F, conductor I8, conductor 20, conductor 26, conductor |02, a back contact of relay MF2, conductor |03, resistance |04, conductor |05, to conductor |00. This ground potential is impressed on conductor |0| which can be traced to the ring lead through conductor |00, a back contact of relay MFI (not operated), conductor 59, conductor 98, contact 15 of relay SAI, conductor 51, contact 58 of relay MF, conductor 52, contact 50 of relay F, conductor FR. to the ring lead of the cord and jack, a back contact of relay BIS of trunk circuit 0, contact 8| of relay KC, and the windings of relays RM, RP and RS to battery 325. The relays in the sender respond to these potentials to register intelligence in a well-known manner.

In a similar manner the other keys of the keyset can be operated to transmit signals composed of current impulses to the sender. If the connected trunk or intertoll circuit is in a class requiring a definite number of digits the key-set will be released automatically on completion of keying in a manner to be described later. If it is a class requiring a variable number of digits, it will not be automatically disconnected. On such calls the KST key will be operated after operation of the numerical registration keys. Operation of the KST key will cause relay ST to operate by reason of a circuit established from the KST key, through conductor |09, through the winding of relay ST, to battery ||0, and thence to ground. Operation of relay ST connects ground through conductor El to the tip conductor of the cord and resistance battery to the ring conductor of the cord to indicate to the sender that no more digits will be keyed. Ground is connected to the tip conductor BI by a circuit traceable from conductor I which is at ground potential, through contact ||2 of relay ST, to conductor |I3 which can be traced to the tip conductor T of sender circuit 1 in a circuit heretofore described. Resistance battery 333 is connected to the ring lead 51 through a circuit extending from lead I I5, upon Which the resistance battery voltage is impressed through contact I I4 of relay ST, to conductor IIB. and then to the ring conductor of sender circuit 1 in a manner heretofore described.

After the last impulse has been transmitted to the sender, the sender circuit 1 connects signaling battery of the same voltage as battery 333 to both the tip and the ring conductors to operate relay P in the key-set circuit. The connection from the ring lead of the front cord can be traced through conductors FR, 52, 51, 98, |20, |2|, |23, and then through winding I1 of relay P to conductors |24, |25, and to negative battery |20. The connection from the tip lead of the front cord can be traced through conductors FT, 5|, 6I, 93, then through winding ||8 of relay P to conductors |24, |25, and then to negative battery |26. Relay P is soconstructed that the biasing winding IIS, when energized, will maintain contact |21 closed unless both winding ||1 and winding I I8 are energized by the aforementioned signaling battery in the sender. circuit 1. Relay P, inoperating, .operates relayKD by clos-` ing contact |29; Relay KD, 'in operating, locks under control of relay F so that after relay P is deenergized, opening contact |29, relay KD remains energized. The locking circuit is traced from ground on conductors 33 through conductors 42,'4I, 39, 38, 31, to the Winding of relay KD, and then to negative battery 36. Operation of relay KD also shuts the biasing winding I I9 of relay P so that it Will hold on either winding I|1 or IIB, and disconnects either the tip 93 or the ring conductor 98 from relay P and connects ground over that lead to the sender, determining whether or not automatic start of machine ringing is required.

If automatic start of machine ringing is required, the operation of relay KD connects conductor FR, through conductor 52, conductor 51, contact 15, conductor 98, conductor |20, contact 16, conductor |2I, contact |30 of relay KD, conductor ISI, contact |32 of relay ME', to ground. The sender interprets this signal in a well-known manner and removes battery from conductors T and R and later transmits a short pulse of ringing current over the trunk to the called ofice.

Where automatic start of machine ringing is not required by the intertoll trunk circuit, the operator manually operates key 202 sor that when relay KD operates, conductor FT is connected through conductor 5|, conductor 6|, conductor 93, contact |33 of manual key 202, conductor |20, conductor |2I, contact |30 of relay KD, conductor I 3|, contact |32 of relay MF, to ground. In this case also the sender disconnects battery from the tip and ring conductors but does not transmit the pulse of ringing current.

When the signaling Ibattery is disconnected from conductors T and R in the sender, relay P releases and contact |21 of relay P is made and contact |29 is broken. Ground potential on the armature of relay P then passes through contact |34 of relay KD, conductor |35, contact |36 of relay SAI, conductor |31, conductor I4, conductor I5, to shunt relay F from its battery source I3. Relay F releases and causes the release of relays KP, SA, SAI and KD by removing ground or battery from their various circuits previously described and releases DI if the talking key has been restored. Release of relay F also extinguishes the KF lamp and the sender S lamp. Since relay SA is released, battery source 333 is removed from thc key-set keys. The circuit is now in its normal non-operating condition except for relay DI which is not released until the talking key has been released.

The foregoing discussion has been devoted exclusively to an instance where the intertoll trunk circuit and its associated y circuits have been adapted to receiving direct current key pulsations, There are instances, however, when a cord circuit is connected to a trunk circuit required to transmit multifrequency key pulses to a sender circuit. The operation of the key-set circuit under such circumstances will now be described in detail.

Let it be assumed that the key-set operator has plugged the front cord into the outgoing trunk circuit 4 and the cord-talking key has been operated, and relays in the position circuit have functioned to connect ground to lead DH and to loop the ground from lead DFI to lead DF. Relay DI is then operated in a manner described previously. Also as described hereinbefore, operation of the iront key pulsing key KPF connects ground on the D F lead to the windings of relays KP and F. Relay KP operates and locks under 9. control of relay F. `Relay KP-is operated at this time to allow time for the core oi the winding to become saturated to stabilize the releasing time of the relay. Relay F, in operating, `(l) lights the KF lamp to indicate that the key-set is associated with the front cord; (2) opens vthe operating circuit for relay R; (3) supplies ground to conductor |92 of the key-set circuit and for locking up relays KD, KP, MF, MFl and IMFZ. SAI KD and KP, have been discussed previously, For relays MF, MF! and MF! the locking grounds may be traced by circuits described later. Returning again to the operation of relay F further results of the operation oi said relay are (4f.) connects ground to lead DH for holding the key pulsing circuit locked to the cord circuit even though the talking` key should be restored tc its normal position; (5) disconnects the tip and ring leads of the cord circuit from the position circuit and4 connects them to the key-set circuit; (S) connects biasing battery 53 through resistance X to relay P; and ('1) connects lil-volt battery i8 through low resistance relay D, conductors 51, 52 and FR to the ring conductor of the front cord. Relay D, in operating, opens the operating circuit for relay Dl. lt will be noted that in the case of direct current key pulsing relay D remained operated for only a short period'of time inasmuch as ,ground Was removed from the ring conductor by operation of relay KC in the solider. The interval of time relay D was operated in the case of direct current key pulsing was insuiiicient to allow slow-to-release relay Di to release. In the case of multifrequency key pulsing, however, the ground 5 placed on the ring conductor is not removed and consequently relay D remains operated and relay DI releases. With relay D operated and relay DI released, ground is connected through contact 49 of relay F, conductor 8, con tact |46 of relay D, contact |ll| of relay Di, conductor HB2, to the winding of relay MF. Relay MF operates, providing multifrequency key pulsing for the connected trunk circuit 4. In operating, relay MF, (l) locks under control of relay F in a circuit extending from ground, through contact I9 of relay F, conductors I8, 26, 2|, |38, contact |39 of relay MF, winding of relay MF, to negative battery H59; (2) closes in part circuits for operating relays KPl, MFl and MFZ. The

part of the circuit closed for operating relay KP| is contact |55 of relay MF, and for relays MFI and MFE it is contact 33| o relay MF. Closing of contacts |5| and |52 of relay MF transfers the tip and ring conductors 5| kand 52, from conductors 6| and 51, respectively', to the repeating coil A in obvious circuits. Operation ci relay MF also releases relay D by opening contact 58, thus removing ground from the winding of relay D. Another function of the operation of relay MF is to open contact |32 a-nd thus remove ground from contact |35 of relay KD so that there is no interference with the disconnect feature of the key-set circuit.

When the iront cord circuit was plugged into the outgoing trunk circuit relay L operated in series with the windings of relays FS and FL in the operators position circuit. The closing of contact 355 completed the winding circuit for relay N. Operation of relay N closed contact 353. The closing lcf contact 353 completed the circuit over the trunk from nega-tive battery' 355 in the called `central oiiice, through the winding of relay 322, a contact of relay 391, conductor 311, conductor 3| l, winding 3H), conductor 303, con- The circuits supplying ground for relays tact 363, conductor 368, Winding 3|.6 of relay P L, conductor SI5, winding 3M, conductorv 3|3, con,- ductor 326, a Contact of relay 3,01, winding .of relay 32,2 to ground. Relay PL doesJ not operate at this time because it is a polarized relay and the current through its winding is in the wrong direc-y tion to operate relay PL. L

The sleeve lead 3|9 may be traced from the. windings of relay L into the position circuit, to the winding of marginal relay FL, then to the winding of relay FS, and then to battery. When the sleeve lead 3 9 can go to ground through the low resistance Winding LR. of relay L, theA marginal relay FL will operate to'place ground on lead FLI so that relay KP| ,may operate. ABut when relay PL is not energized, then sleeve lead 3|9 must go to ground through the high resistance Winding HR of relay and kmarginal relay FL will not operate. Therefore no ground is vapplied to lead FL! and relay KP| will not operate. This is the situation existing before relay PL has operated. When a sender is attached to .the trunk circuit IT in the called cnice relay 3|l1 is energized and the current through the winding .or relay PL is reversed by virtue of the conductors 320 and 3|-1 being interchanged'with respect to the battery 306. Operation of relay PL closes contact 323 of relay PL thus placing ground on the low resistance winding of relay L which allows marginal relay FL to operate and place ground on lead FLI. For a full' and detailed de-` scription of the trunk circuit and associated link circuits, sender, and key pulse Vreceiving circuit, reference is made to United States Patent -2,288,- 251, granted to P. B. Murphy on June 30, 1942. After ground is placed on lead FLI the cord lamp FL lights and relay KP| operates in a circuit exe tending from 24-volt negative battery |53, through the winding of relay KP|, conductor |54, contact |55 of relay KP, conductor |56, contact of relay MF, conductor |51, conductor |58, gnltact |59 of relay F, to ground on conductor Relay KP|, in operating, connects repeating coil A through conductors |60 and |6| to tone sources f and c, thereby transmitting a key pulsing signal over the trunk to the sender in the called office. The key pulsing tone signal is a signal to the sender. The numerical keys are not connected to the repeating coil during tranSmiS- sion of the key pulsing tone signal so as to prevent this tone signal from being mixed with the other tone signals should the operator key prematurely. The key pulsing tone signal circuit may be traced from repeating coil A, through conductor |62, contact |63 o f relay KP|, conductor |60, tone source f, tone source c, conductor |61, conductor I6 I contact |65 of relay KP|., -con,- ductor |66, and back into repeating coilA. From repeating coil A the signal is transmitted over the tip and ring leads of the cord, A,through'the repeating coil of outgoing trunk circuit 4, over the trunk to the called cnice, through therepeating coil of incoming trunk circuit IT., .and then to the attached sender. Returning to the operation of relay KP|, operation ,Of vsaid relay KP| opens, in part, the operating circuit for relays AMFI and MF2 by opening contact |45 and opens the locking circuit for relay KP by Open# ing contact 21. Assuming that the 'key pulsing key KPF has been released, relay KP releases slowly and opens the operating path for relay KP| by opening contact of relay KP. The slow release of relay KP is to insure that the KP tone leads are connected to the repeating coil -A long enough to satisfy 4the sender.

Relay KPI, in releasing, transfers the tip |82 and ring |06 leads from the tone sources f and c to conductors |68 and |64, respectively. In addition, the release of relay KPI completes the circuit for operating relays MFI and MF2 in a circuit extending from the windings of relays MFI and MF2, through conductor |46, contact |45 of relay KPI, conductor |44, contact |43 of relay KP, conductor 332, contact 33| of relay MIF', conductor 330, conductor I 69, contact |10 of relay KD, and through contact I 9 of relay F to ground.

Relays MFI and MF2, in operating, transfer the leads of the numerical keys 83 through 92 from the battery 333 and ground supplies used for direct current pulsing to the tone sources required for multifrequency pulsing. This latter is accomplished by closing contacts I1|, |12, |13, |14 and |15 of relay MFI and contacts |16, |11, |18, 19 and |80 of relay MFZ. The closing of contacts |8| and 334 of relay MFI connects the repeating coil A to the key-set, which is in readiness for the transmission of key pulsing signals. Contact |82 of relay MFZ also closes to complete the circuit for relay SAI. Said circuit extends from negative battery 35, through the winding o f relay SAI, conductor 28, conductor I 83, contact I 82 of relay MF2, conductor |84, conductor |69, contact |1IJ of relay KD, to ground on conductor 33.

Relay SAI, in operating, closes contacts 14, 15 and 16 in preparation for the later operation of relay P, and closes contact 80 which lights the sender lamp S by completing a circuit hereinbefore described and informs the operator that keying may be initiated.

The operator may now operate the keys corresponding to the code number desired. Various combinations of alternating current signals are sent out to the trunk circuit. One of these circuits wlll be traced as an example. Let it be assumed that key 85 is depressed. Conductor 91 is connected to conductor 96 and conductor |0I is connected to conductor |06. A circuit may now be traced from alternating current source a, through conductor |86, conductor |65, contact |13 of relay MFI, conductor 10, conductor 91, conductor 96, conductor 95, contact |8| of relay MFI, conductor |68, conductor |62, coils of repeating coil A, conductor |66, conductor |64, contact 334 of relay MFI, conductor |00, conductor IOI, conductor |06, conductor |88, conductor |89, contact |19 of relay MF2, conductor |90, conductor |61, alternating current source c, to alternating current source a. Similar circuits for other keys may be traced. The repeating coil A carries the two alternating current frequencies to the trunk circuit and the receiving circuit associated with the sender responds to these signals and causes the code and number to be registered in the sender.

After the operator has completed registration she will wish to release the key-set. This may be accomplished by operation of the KST- key which completes the circuit for the winding of relay ST described before herein, and will operate relay ST. Relay ST, in operating, connects alternating current sources e and j to repeating coil A through circuit connections extending from conductor -|66, through conductor |64, conductor I9| contact |92 of relay ST, conductor I 93, conductor |94, alternating current source e, alternating current source f, conductor |95, contact |96 of relay ST, conductor |91, conductor |68, to repeat# ing coil A. This signal will indicate to the sender that no more digits will be keyed. Operation of` 12 relay ST also connects battery 333 through resistance |01 to windings ||1 and I I8 of relay P to operate relay P.

Relay P operates and in operating, operates relay KD by'means of a circuit extending from ground, through the armature of relay P, contact |29 of relay P, conductor |28, conductor 31, winding of relay KD, to negative batteryI 36. Operation of relay KD also opens the circuit through winding I I1 of relay P by opening contact I 22 and shunts winding ||9 of relay P by closing contact |98. When relay KD operates, it closes a locking circuit extending from the Winding of relay KD, through conductor 31, conductor 38, conductor 39, contact 40 of relay SAI, conductor 4I, conductor 42, contact 43 of relay KD, to ground on conductor 33. This ground is under control of relay F as was described previously.

When the operator releases the KST key, relay ST releases,k tone sources e and f are disconnected from repeating coil A, and resistance battery is disconnected from the primary and secondary windings I I 1 and I I 8 of relay P to release relay P. Release of relay P closes a circuit connection from ground, through the armature of relay P, Contact |21, conductor |99, contact I 34 of relay KD, conductor |35, contact |36 of relay SAI, to conductor I 3l. This circuit connection shunts relay F and consequently causes the release of relay F. As described in the case of direct current key pulsing, the release of relay F removes ground or battery from all the relays and they all therefore release except relay DI. Lamps KF and S are extinguished and the cord circuit is reconnected to the position circuit. The key-set circuit is in its normal position.

If the operator should depress any of the numerical keys before the sender lamp S lights, in the case of direct current key pulsing, or before relay MFI operates, in the case of multifrequency key pulsing, ground will be applied from the keyset to relay KD. In the case of direct current key pulsing this ground may be traced from contact I9 of relay F, through conductors I8, 20, 26, |02, and then into al1 of the keys. Operation of any key places ground on lead 35 which can be traced through conductors 95, 94, and 93, contact 13 of relay SAI since relay SAI will not yet be operated, conductor 38, conductor 31, to relay KD. In thecase of multifrequency key pulsing, the ground will be momentarily applied to relay KD in a similar manner. After relay MFI is operated, however, lead no longer can be traced to the winding of relay KD and therefore no ground would be applied to relay KD should the operator key prematurely. Relay KD locks under control of keys KPR and KPF, and closes contact 200 connecting the sender lamp S to the |23-impulses per minute interrupter circuit 20|, thus flashing the lamp. To restore the key-set circuit to apuising condition, either key pulsing key KPF or KPR is momentarily operated, releasing relay KD by momentarily removing ground therefrom. In releasing, relay KD closes a, circuit for operating relay SAI provided a sender has been' found in the meantime and relay SA, in thc case of-,direct current key pulsing, or relays MFI andlVlFZ, in the case of multifrequency key pulsing, has been operated.

In ca se of trouble arising, the operator may pun down the cord to which the key-set is attached, causing the position circuit to open the loop between leads DFI and DF or DRI and DR to release relay F or R, respectively, which, in releasing,

accuses' i3 restores the circuit to normal in a manner'hereinbefore described.

What is claimed is:

l. In a telephone system, a key-set circuit, comprising a set of digit keys,A a plurality of trunk circuits, a first number of said trunk circuits each including means for supplying and applying to said key-set circuit a iirst set of electrical conditions indicating that a first type of key impulses is to be transmitted over each of said rst number ci trunk circuits by said key-set circuit, a second number of said trunk circuits each including means for supplying and applying to said key-set circuit a second set of electrical conditions different from said first set of electrical conditions and indicating that a second type of key impulses is to be transmitted over each of said second number of trunk circuits by said key-set circuit, means including a cord circuit for connecting said keyset circuit to any one of said trunk circuits, a rst transmitting means included Within said key-set ircuit and comprising first voltage sources and said digit keys for transmitting said first type key impulses, a second transmitting means included within said key-set circuit and comprising second voltage sources and said digit keys for transmitting said second type key impulses, means responsive to said sets of electrical conditions comprising testing relays for determining Whether a trunk circuit to which said cord circuit is connected is one of said first number or one of said second number of trunk circuits, and means controlled by said determining means for connecting said rst transmitting means to the any one of said first number of trunk circuits to which said cord circuit is connected, and for connectiigig said second transmitting means to any one of said second number of trunk circuits to which said cord circuit is connected.

2. 1n a telephone system, a plurality ci cord circuits, a first number of trunk circuits each including means for supplying and applying a first set of electrical conditions to any connected one of said cord circuits, said first set of electrical conditions indicating that a trunk circuit is arranged to transmit direct-current key impulses, a second number o trunk circuits each including means for supplying and applying a second set of electrical conditions to any connected one of said cord circuits, said second set of electrical conditions indicating that a trunk circuit is arranged to transmit alternating-current impulses, and a key-set circuit comprising a set of numerical keys, direct-current sources, alternating-current sources and means including testing relays selectively responsive to said different sets of electrical conditions for connecting said direct-current sources to said numerical keys to enable the transmission of direct-current key impulses through a connected cord circuit to one of said first number of trunk` circuits responsive to actuation of any one of said keys, and for connecting said alternatingcurrent sources to said numerical keys to enable the transmission of alternating-current key impulses through a connected cord circuit to one of said second number of trunk circuits responsive to actuation of any one of said keys.

3. In a telephone system, jack-ended trunk lines including a first group of trunk lines requiring direct-current key impulses to be transmitted thereover and a second group of trunk lines requiring alternating-current key impulses to be transmitted thereover, a plurality of cord 14 circuits .each for connecting to any one of said trunk lines, a key-set circuit including a key-set for encoding information into electrical impulses to be transmitted over any cord circuit to a .connected one of said jack-ended trunk lines, means comprising direct-current voltage sources and said key-set included in said key-set circuit for transmitting direct-current impulses over a cord circuit to any one of said first group of trunk lines when said cord circuit is connected thereto, and means comprising alternating-current Voltage sources and said key-set included in said keyset circuit for transmitting alternating-current impulses over a cord circuit to any one of said second group of trunk lines when said cord circuit is connected thereto.

e. In a telephone system. jack-ended trunk lines comprising a first group of trunk lines capable of being connected to apparatus operated by direct-current key impulses and a second group of trunk lines capable of being connected to apparatus operated by alternating-current key impulses, a cord circuit for connecting to any one of Asaid jack-ended trunk lines, a key-set circuit including a set of keys for encoding information into electrical impulses to bev transmitted through said cord circuit to a trunk line, means including selectively responsive relay means in said key-set circuit for distinguishing between said rst group of trunk lines and said second group of trunk lines, means comprising `direccurrent voltage sources connected to said set of keys and controlled-by the said selectively responsive relay means for enabling the transmission of direct-current key impulses through the said cord circuit to a trunk line if said trunk line is connected to apparatus operated 'by direct-current key impulses, and means comprising .alternating-current voltage sources' connected to said set of keys and controlled by the said selectively responsive relay means for enablingv the 'transmission of alternating-current impulses through the said cord circuit to a trunk line if said trunk line is connected to lapparatus operated by alternating-current key impulses.

5. In a telephone system, an operators position, a cord circuit, a rst group of trunk circuits each including means for supplying and applying to said operators position through said cord circuit a first set of electrical conditions indicating that direct-current impulses are to be transmitted over each of said trunk circuits in said first group, a second group of trunk circuits each including means for supplying and applying to said operators position through said cord circuit a second set of electrical conditions indicating that alternating-current impulses are to be transmitted over each of said trunk circuits in said second group, and a key-set circuit comprising a key-set for encoding information into electrical impulses, a direct-current source, a multifrequency alternating-current source and relay means for alternatively connecting the one or the other of said sources to said key-set; said relay means being selectively responsive to the different sets of electrical conditions applied by each trunk circuit of the said first and the said second groups of trunk circuits to enable said key-set circuit for the transmission of the type of key impulses required by a trunk circuit connected to said operators position by said cord circuit.

`B. In a. telephone system, a plurality of cord circuits, a key-set circuit including a set of keys for encoding information into electrical impulses,

15 a rst number of trunk circuits each including means for supplying and applying through a cord circuit a continuous potential condition to said key-set circuit and said continuous potential condition indicating that multifrequency altermating-current key impulses are to be transmitted by said key-set circuit, a second number of trunk circuits each including means for supplying and applying through a cord circuit a momentary potential condition to said key-set circuit and said momentary potential condition indicating that direct-current key impulses are to be transmitted by said key-set circuit, a direct-current key impulse source in said key-set circuit, a multifrequency alternating-current key impulse source in said key-set circuit, means in said key-set circuit comprising testing relays selectively responsive to said continuous and inom'entary potential conditions for determining Whether any one of said jack-ended trunk circuits to which a cord circuit is connected is one of said irst number or one of said second number of jack-ended trunk circuits, means in said key-seat circuit controlled by said determining means for connecting through a cord circuit said multifrequency alternating-current impulse source to said keys to enable the transmission of multifrequency alternating-current key impulses to any one of said rst number of jackended trunk circuits, and means in said key-set circuit controlled by said determining means for connecting through a cord circuit said directcurrent impulse source to said keys to enable the transmission of direct-current key impulses to any one of said second number of jack-ended trunk circuits.

7. In a multioice telephone system, and operator position in one office, trunks from said one office to other ofiices, a key-set lcircuit at saidA position comprising a set of digit keys and directcurrent and alternating-current sources for transmitting either direct-current or alternat-.

current coded digit impulses over any one of said trunks, means comprising a cord for connecting said key-set circuit to any one of said trunks, a

first group of said trunks extending t0 an oince arranged to receive direct-current coded digit impulses, a second group of said trunks extending to an oce arranged to receive alternatingcurrent coded digit impulses, means in each of said rst trunks for connecting a first electrical potential through said cord to said key-set circuit to indicate that direct-current coded digit impulses are to be transmitted over any connected one of said first trunks, means in each of said second trunks for connecting a second electrical potential to said key-set circuit to indicate that alternating-current coded digit impulses are to be transmitted over any connected one of said second trunks, and means comprising testing means in said key-set circuit selectively operated upon connection of either of said first and second electrical potentials thereto to connect said direct-current source to saiddigit keys when said key-set circuit is connected to one of said rst trunks thereby to effect the transmission of direct-current coded digit impulses over the connected one of said rst trunks responsive to the actuation of any digit key and to Iconnect said alternating-current source to said digit keys when said key-set circuit is connected to any one of said second trunks thereby to effect the transmission of alternating-current coded digitv impulses over the connected one of said second trunks responsive to the actuation of any digit key, the digit code thus transmitted over the connected one of said trunks depending upon the digit key which is actuated.

BURTON MCKIM.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Dato 1,914,358 Brooks June 2G, 1953 2,153,129 Bascom Apr. 14, 1939 2,188,467 Wochinger Jan. 30, 1940 2,288,251 Murphy June 30, 1942 

